1. Field of the Invention
The present invention generally relates to the signal detecting techniques, and it particularly relates to method and apparatus for detecting if the received signals contain a predetermined signal, and transmitting apparatus and receiving apparatus utilizing the same.
2. Description of the Related Art
As a spread spectrum communication system using the radio frequency of 2.4 GHz band, the wireless LAN (Local Area Network) of IEEE802.11b standard has been developed and put to practical use. This wireless LAN realizes the maximum transmission rate of 11 Mbps by CCK (Complementary Code Keying) modulation. The signals, such as preambles or headers, which contain control signals therein are produced by spreading DBPSK- or DQPSK-modulated signals with spread codes. Here, DBPSK stands for Differential Binary Phase Shift Keying and DQPSK Differential Quadrature Phase Shift Keying. A receiving apparatus in the spread spectrum communication system like this is generally provided with a matched filter. The matched filter outputs correlation values of the received signals and the spreading codes. When the received signals are inputted continuously to the matched filter, large correlation values are outputted in constant cycles. Upon receiving such a large correlation value, the receiving, apparatus judges that the received signal is a signal to be processed, and then it carries out the receiving processing of received signals. The receiving apparatus also carries out the timing synchronization in the receiving processing, based on the timing at which the large correlation value is detected (See Reference (1) in the following Related Art List, for instance).